Like fifty doubled up in merriment? (5)
I believe the answer is:
jolly
'up in merriment?' is the definition.
'jolly' can be an answer for 'up' (I've seen this before). I am unsure of the 'in merriment?' bit.
'like fifty doubled' is the wordplay.
I cannot really see how this works, but
'like' could be 'ly' (similar in meaning) and 'ly' is present in the answer.
'fifty' could be 'l' (Roman numeral) and 'l' is located in the answer.
The remaining letters 'jo' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for jolly that I've seen before include "Good-humoured, cheerful" , "Very - jovial" , "all-expenses-paid trip" , "Royal Marine (slang)" , "Mirthful" .)